Aneuploidy

Aneuploidy is the name given to the increase or decrease of a chromosome in the genome. Down syndrome is an example of aneuploidy.
The human genome has several genes, which are arranged in chromosomes. Humans have 23 pairs of chromosomes, with 22 pairs of autosomal chromosomes and one pair of sex chromosomes. In women, the sex chromosomes are X and X; in males, they are X and Y. Sometimes, however, chromosomal aberrations occur. One such aberration is aneuploidy .

→ What are chromosomal aberrations?

Chromosomal aberrations are changes in the number of chromosomes or their structure . These changes, even if small, can profoundly affect the development of the embryo, cause anomalies in the carrier and, in some cases, death.

These changes occur relatively frequently. It is estimated that 8.1% of all pregnancies have some chromosomal aberration and that it is responsible for about half of the cases of miscarriage.

→ Numerical chromosomal aberrations

Numerical chromosomal aberrations cause loss or excess of entire chromosomes. They fall into two categories: euploidies and aneuploidies.

→ Aneuploidies

Aneuploidies are changes in the number of chromosomes that are characterized by the loss or gain of one or more chromosomes in the genome. They are the most frequently observed chromosomal abnormalities.

They usually occur as a result of a nondisjunction error (problem in the segregation of homologous chromosomes or sister chromatids) during maternal cell meiosis, and may also occur in paternal meiosis, which is less common. The most common aneuploidies are those that have an extra chromosome (trisomy) or the deletion of a chromosome (monosomy).

→ Examples of aneuploidies

The karyotype above shows the presence of an extra chromosome 21

  • Down syndrome : it is a chromosomal abnormality in which an extra chromosome 21is observed, being, therefore, a trisomy. This increase in the number of chromosomes causes the appearance of very striking characteristics in its bearer, such asmental retardation, round and flat face, almond-shaped eyes, short and broad hands, limited growth, slanted palpebral fissures and muscular hypotonia. In addition to these visible characteristics, we must highlight that patients with the syndrome are at increased risk of heart and respiratory diseases.
  • Turner Syndrome : Loss of an X chromosome occurs. Patients with this condition usually have ashort stature, webbed neck, low set of ears and hair, scoliosis and kyphosis, infantile genitalia, atrophied ovaries, primary or secondary amenorrhea, and mental retardation. Light.
  • Klinefelter syndrome : there is an increase in an X chromosome in the patient. Usually, the signs of the problem are more evident after puberty. Among the signs, we can mention:gynecomastia(swelling of male breast tissue),hypogonadism(the glands produce little sex hormone),infertility, underdevelopment of secondary sexual characteristics and behavioral delay.

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